Conventionally, as disclosed in U.S. Pat. No. 4,946,107 and JP-A-11-500509 (U.S. Pat. No. 5,769,391), a fuel injection valve has a fixed core that is mounted on the opposite side of a jet nozzle with respect to a moving core. The fixed core is opposed to the moving core to form a magnetic circuit with the moving core. The fixed core extends toward a fuel inlet to form a fuel passage. However, in this construction, the fixed core extends in the axial direction, and manufacture of the fixed core is difficult.
A fuel injection valve may have a pipe member that is separate from a fixed core to cover the outer peripheries of both a moving core and a fixed core to form a fuel passage.
For example, a fuel injection valve 200 shown in FIG. 7 includes a pipe member 202 that covers both the outer peripheries of a moving core 212 and a fixed core 214. The moving core 212 reciprocates with a valve member 210. The fixed core 214 is mounted on the opposite side of the valve member 210 with respect to the moving core 212. The pipe member 202 includes a first magnetic pipe 203, a non-magnetic pipe 204, and a second magnetic pipe 205 in this order from the side of the moving core 212. The first magnetic pipe 203 and the non-magnetic pipe 204 are joined together by welding or the like, and the non-magnetic pipe 204 and the second magnetic pipe 205 are joined together by welding or the like. The non-magnetic pipe 204 is mounted in a manner to cover the outer periphery of a gap 216 formed between the moving core 212 and the fixed core 214 to prevent magnetic flux from short-circuiting between the first magnetic pipe 203 and the second magnetic pipe 205. The first yoke 230 and the second yoke 232 cover the outer periphery of a coil 220 mounted on the outer periphery of the pipe member 202. Both the yokes are connected magnetically to each other. The first yoke 230 is connected magnetically to the first magnetic pipe 203, and the second yoke 232 is connected magnetically to the second magnetic pipe 205.
However, the pipe member 202 is axially constructed of three members, that is, the first magnetic pipe 203, the non-magnetic pipe 204, and the second magnetic pipe 205. The pipe member 202 extends over the locations, in which the pipe member 202 connects to both the first yoke 230 and the second yoke 232. As a result, parts of the pipe member 202 are increased in number. Besides, joint portions, in which the parts of the pipe member 202 are joined together, are increased. Accordingly, manufacture of the pipe member 202 becomes difficult.
Besides, both the magnetic members constructed of the first magnetic pipe 203 and the second magnetic pipe 205 may cover both the outer peripheries of the moving core 212 and the fixed core 214 as shown in FIG. 7. In this structure, the area of the magnetic portions, which cover the outer peripheries of the moving core 212 and the fixed core 214, are increased. Therefore, magnetic flux, which flows among the coil 220, the moving core 212 and the fixed core 214 through the first magnetic pipe 203 and the second magnetic pipe 205, is increased. That is, magnetic flux flowing through the gap 216 between the moving core 212 and the fixed core 214 is decreased. As a result, force of magnetic attraction may be reduced. Besides, magnetic portions, which cover both the outer peripheries of the moving core 212 and the fixed core 214, are increased. Accordingly, rising and falling responsiveness of the force of magnetic attraction may be degraded when electric current supplied to the coil 220 is made ON and OFF. Thus, valve opening and closing responsiveness may be degraded. This is the same also with the case where the whole pipe member 202 is formed from a magnetic material.
Conversely, when the whole pipe member 202 is formed of a non-magnetic material, the valve-opening responsiveness may be degraded because magnetic resistance becomes large and the force of magnetic attraction is reduced.